1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or printer.
2. Description of the Prior Art
The present invention applicant has already proposed postprocessing apparatuses in Japanese Patent Application Nos. 2001-318075 and 2001-281315, which collate many sheets on which images are formed by an image forming apparatus body having an electrophotographic copying machine, printer, or the like for each print count, and bookbind the sheets by binding them together by using binding means or perform a three-fold process.
This postprocessing apparatus is connected to the image forming apparatus body and can perform predetermined postprocessing for sheets on which images are formed by the image forming apparatus body.
The predetermined postprocessing includes binding processes, folding processes, and the like. More specifically, the binding processes include an end binding process performed by a binding means to bind the end portions of sheets together and a saddle stitching process performed by the binding means to bind the middle portions of sheets together. The folding processes include a center folding process of folding a sheet along its center and a three-fold process of folding a sheet in three.
In the above folding process, in order to perform predetermined postprocessing for sheets on which images are formed by the image forming apparatus body, a predetermined convey method is used as a method of conveying the image-formed sheets to the postprocessing apparatus.
As a form of delivering a sheet from the image forming apparatus body to the postprocessing apparatus, either one of the following forms of delivery is used: face-up delivery of delivering the sheet with its image-formed surface facing up; and facedown delivery of delivering the sheet with its image-formed surface facing down.
In the above three-fold process as well, therefore, sheets are delivered with facing down for the three-fold process that is performed with a high frequency as in the case of letters inserted in envelopes, and each sheet is folded in three with the image-formed surface (upper surface) facing outward, ire., the non-image surface (lower surface) facing inward.
Although a three-fold process can be performed for letters and the like, a letter to be inserted into an envelope is preferably folded in three with its image-formed surface (upper surface) facing inward. However, such a three-fold process for letters and the like cannot be done.
That is, the conventional apparatus can perform a three-fold process only in one form, but cannot perform it with an arbitrary one of the upper and lower surfaces of a sheet facing inward.